CA2064085A1 - Combined bias supply and power shut-off circuit - Google Patents

Abstract

A microcircuit bias-current supply (10) in a wristwatch-pager (12). An FM-radio receiver in a microcircuit paging device operates intermittently with a short on-time and long off-time to reduce power consumption and preserve battery life. The bias-supply circuit (10) distributes predetermined bias currents to a plurality of functional circuit areas (12) of the microcircuit die, the bias currents being disabled during off-time of the receiver such that the current drain of the entire microcircuit is virtually zero, being in the range of nanoamps. The inefficiencies and disadvantages of a series switch power on and off are eliminated by providing a plurality of switched current sources (44a-44n) which perform the dual function of circuit biasing and current switching.

Description

W09l~0l594 PCT/US90/03946 20~408~

2 Field of the Invention

3 The present invention relates to electronic circuitry and

4 more particularly to power shut-off circuitry and to current bias circuitry.

6 Background of the Invention 7 Electronic paging systems incorporating portable, battery 8 operated paging receivers use various methods for 9 reducing the power consumption of the receivers to minimize their overall size and to extend battery life.
11 Many of the existing systems supply power to the receiver 12 circuits only during intermittent and/or predetermined 13 time periods during which data for the receiver is 14 transmitted. ~he problem of limiting power consumption and extending battery life is exacerbated in miniature 16 radio receivers incorporated in a wristwatch-pager such 17 as that described in U.S. patent 4,713,808 to Gaskill et 18 al. The small size and portable nature of the wristband 19 receiver, plus the large number of circuits used compared with the number used in a conventional electronic watch, 21 make reduced power dissipation a primary consideration in 22 the design of the wristwatch-pager.~

23 In the system described in the GaskiIl patent the duty 24 cycle of the radio receiver is very short, hence, in order to Pxtend battery life it is desirable that power 2064~8~ 2 l dissipation in the receiver circuits be virtually zero 2 during the relatively long periods when the receiver is 3 inactive. Further, it is desirable that the circuits 4 involved be insensitive to decreases or fluctuations in power supply voltage caused by battery age, power on/off 6 cycling, the resistance of interconnecting power leads, 7 etc.

8 A conventional method for switching power to a circuit 9 utilizes a switching device such as a series pass transistor; however, there are several disadvantages ll associated with such circuits. A series pass device, in 12 the on state, has an associated voltage drop that 13 subtracts from the available supply voltage. Such 14 voltage drop is significant in low-voltage, battery operated apparatus.

l6 Furthermore, the current must be consumed in the 17 controlling element of a power switching device, e.g., 18 the base current required to saturate a switching l9 transistor is greater than the collector current divided by beta. In the case of a low-beta pnp switching device 21 implemented in-a typical-bipolar integrated circuit 22 process optimized for npn devices, the base current of 23 the switching device can be a significant percentage of 24 the total current, and this current is essentially wasted.

., .

WO91/01~94 PCr/US90/03946 3 20~q85 l Another disadvantage of using a geries switching devices 2 is that the die area required for a swi~ching device that 3 carries the total chip current is significant.

4 A separate, off-chip switching transistor could be used to improve beta at the cost of an additional part and 6 more board area. An npn switching device could be used 7 to reduce the base current demand, but such a device 8 would require a base voltage above the battery voltage 9 for a low collector-emitter voltage VCE drop if the switching device were placed between the battery positive ll terminal and the load. It is noted that if a pass device 12 were placed in the ground return path, its VCE drop could 13 adversely affect ground-referenced signals.

14 The object of the present invention to provide an improved on-off switching circuit that maximizes battery 16 life.
' -17 Another object of the present invention~to eliminate the18 need for a series switching device and thereby eliminate l~ the voltage drop normally associated with such a device.

Yet another object of the present invention is to provide 21 an on-off switch for electronic circuitry which requires 22 little or no power in the off state. -~

WO91/01ss4 PCT/US9~/03946 2061~8~

1 It is another obj ect of the invention to provide an 2 improved bias supply cir-uit for a system which has a 3 short duty cycle followed by a relatively long power-off 4 time.

Another object of the instant invention is to provide an 6 improved microcircuit bias supply with on-off switching 7 control that results in virtually zero current drain from 8 the circuits during quiescent periods.

9 Summary of the Invention The present invention combines in a novel way an on-off-11 switch and the current bias supply circuits for a number 12 of functional circuits. With the present invention, a 13 very small supply independent current source is switched 14 by the external on-off signal. The switch which controls the small independent current source is configured so 16 that the switch draws no current in the off state. The 17 small independent current source in turn controls a 18 ,temperature stable reference voltage source through a 19 current mirror. The output of the-reference voltage source controls a plurality of master current sources.
21 These master current sources in turn control functional 22 circuit;current bias supplies through current`mirrors.
23 Thus when an "on" or,"off" signal-is received from an 24 external source, (a),the small independènt current-source is switched "on" or "off" which in turn (b) switches the ~6 temperature stable reference source "on" or "off" which .

W O 91/01594 P Cr/US90/03946 20~408~
1 (c) switches the master current sources "on" or "off", 2 which in turn (d) controls the functional circuit current 3 bias supplies.

4 The major advantages of the present invention is that it S draws no current in the "off" state and that it does not 6 have a series switch with the associated voltage drop.
7 The functional circuit current bias supply circuits are 8 controlled from the voltage reference through current 9 mirrors and hence they operate at a voltage which is relatively near ground potential. The entire supply 11 voltage (except for the drop across the bias supply 12 circuits) is available to the application circuits.

13 Brief Descri~tion of the Drawing 14 While the invention is set forth with particularity in the appended claims, other objects, features, the 16 organization and method of operation of the invention 17 will become more apparent, and the invention will best be 18 understood by referring to the following detailed 19 description in conjunction with the accompanying drawing in whicho , 21 FIG. 1 is;a.schematic block diagram of a microcircuit 22 bias-current supply and user circuits in accordance with 23 the instant invention; - --~ ^

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WO91/01594 PC~/U~90/03946 206~085 6 1 FI5. 2 is a schematic illustration of a microcircuit chip 2 mounted on a watch-sized printed circuit board and 3 incorporating the circuits of FIG. l;

4 FIG. 3 is a schematic diagram of the bias-current supply circuits of FIG. 1; and 6 FIG. 4 shows an alternative embodiment of the remote 7 current mirror circuit 26a of FIG. 1; and 8 FIG. 5 is a timing diagram of bias current shut-off in 9 accordance with the present invention.

Description of the Preferred Embodiments 11 Referring now to the various views of the drawing for a 12 more detailed description of the components, materials, 13 construction, function, operation and other features of 14 the instant invention by characters of reference, FIG. 1 shows a bias circuit 10 supplying bias current to a 16 plurality of system functional circuits 12, which in the 17 presently described embodiment of the invention comprise 18 the bipolar integrated-circuit components of a miniature 19 FM subcarrier receiver in a wristwatch-pager as described in the aforementioned patent to Gaskill et,al. Operating ~, . ~
21 voltage Vcc is supplied~to the bias circuit~l0 and the 22 system circuits 12 directly from a battery-14:on a bus 23 18; battery voltage is suitably 2.2 to 3.5 volts.

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7 20g408 1 Referring to FIG. 2 in conjunction with FIG. 1, the 2 system functional circuits 12 of FIG. 1 are shown as a 3 plurality of functional circuit areas 20a..n of an 4 integrated circuit chip 21, which can for example be mounted on a printed circuit board (PCB) 22, the bias 6 circuit 10 being located among the circuit areas 20a..n 7 to allow convenient distribution of bias-currents. A
8 functional circuit can ~e any circuit such as a logic 9 gate, an amplifier or a bistable. A functional circuit area means a group of microcircuit elements that make up 11 one or more functional circuits that perform a particular 12 function and by design can be conveniently grouped 13 together in a particular area of an integrated circuit 14 die. A microcircuit element means an integrated-circuit component such as a resistor or a transistor; a 16 microcircuit means at least one functional circuit on an 17 integrated circuit die and formed from interconnected 18 microcircuit elements. Such microcircuit elements could, 19 for example, form a functional circuit area comprising an IF strip, an audio amplifier or a storage matrix. For 21 simplicity, only representative portions of the PCB 22 22 and the interconnzcting conductors are shown.

. .
23 Transistor current sources are commonly used in-analog 24 integrated circuits as biasing elements,~ which results in reduced sensitivity of circuit performance to power-26 supply variations and to temperature. Further, current 27 sources often utilize less die area than resistors to , ............................................... . .

WO9!/01~94 PCT/US9~/03946 2~0~

1 provide the desired bias current, particularly when the 2 required ~alue of bias current is small. As indicated in 3 FIG. 1, when power is enabled in the presently described , 4 embodiment of the invention, the system circuits 12 collectively require about 15 milliamps of current. Each 6 of the circuit areas 20a..n is connected internally of 7 the area by a lead 23a..n to a current source 24a..n, one 8 of which is illustrated symbolically in FIG. 1 as one 9 element 24a of a current-mirror circuit 26a.
Corresponding current-mirror circuits (not shown) such as 11 the circuit 26a are provided in each of the plurality of 12 circuit areas 20a..n. The current source 24a mirrors a 13 second current source 28a of the current-mirror circuit 14 26a, as described in more detail below. Each of the current-mirror circuits 26a..n in the various circuit 16 areas 20a..n is connected by a lead 30a..n to a 17 corresponding current mirror circuit 32a..n in the bias 18 circuit 10.

. .
19 Power is applied to the system circuits by way of a power-enable control signal PWRUPl on a lead '34 from a 21 microprocessor (not shown) that controls system-power.
22 The PWRUPl signal is a CMOS digital logic level, which 23 controls a switch circuit 36 in the ground retu`rn'of a "

24 suppl~-independent,current source 38. A supply- `-'' -independent current source is one in which the bias -26 currents of the circuit are dependent on a voItage 27 standard other than the supply voltage, for example a WO 91/01594 PCr/US90/03946 9 ` 20~408~
Zener diode or the base-emitter voltage VE~E of a 2 tr~nsistor. In the instant embodliment, the best-mode 3 supply-independent current source is a bootstrap or self-4 biased current source 38, which clevelops a current that

5 is made to depend directly on the output of the current

6 source itself, thereby establishing a reference current

7 that is relatively independent of power supply voltage.

8 The current developed in the bootstrap current source 38

9 is mirrored in another current source 39, the current

10 sources 38, 39 together forming a current-mirror circuit

11 40, the output of which is supplied to a band-gap refer-

12 ence circuit 42. The band-gap circuit 42 develops a

13 temperature-stable reference voltage of 1.21 volts, which

14 is distributed to a plurality of master current sources

15 44a..n in the bias circuit 10. Each of the master

16 current sources 44a..n includes an on-chip current-

17 setting resistor 46a..n, and is coupled to a

18 corresponding one of the current-mirror circuits 32a.. n. `

19 Referring momentarily to FIG. 2, the bias circuit 10 is

20- centrally located among the other functional circuit

21 areas 20a..n, and while the band-gap voltage could be

22 distributed to the circuits 20a..n, i~ would be

23 susceptible to vo~:tage drops from resistance~-in leads,

24 noise, etc. However, when currents of predetermined

25 magnitude for each of the functional microcircuit areas

26 20a..n are distributed throughout the system, the , . .

WO9l/01594 PCT/US90/0394b 206~5 lO
1 importance of voltage drops is muted. Current sources 2 32a..n have a high-impedance output, and resistance in 3 the lines 30a..n does not affect the magnitude of the 4 currents. At the various points of use throughout the device, the current is again mirrored, in each instance 6 in one of the current mirror circuits 26a..n. Although 7 the bias currents are remotely re-mirrored in the 8 functional circuit areas, it is seen that a bias current 9 could be supplied directly to a functional circuit locally from the bias supply lO, for example by the 11 current source 46.

12 Referring to FIG. 3, a detailed schematic diagram shows 13 the circuits of FIG. 1, which are implemented in a 14 bipolar integrated circuit. The switch circuit 36 comprises a substrate-contact 16 diffusion transistor 50 which has good saturation 17 characteristics. Transistor 50 has its base connected 18 through a lOOK resistor 51 to ground, and through another 19 lOOK resistor 52 to the PWRUP1 signal input lead 34. The transistor 50, when enabled by the PWRUP1 signal, 21 provides a ground return for the bootstrap current source 22 circuit 38 at a node 56. - ~

23 The bootstrap current source 38 comprises a first lateral 24 pnp (LPNP) transistor 57 having its emitter connected through a lK resistor 58 to the supply~voltage Vcc, a 26 second LPNP transistor 60 and a diode-connected LPNP

Wogl/01594 PC~/I)S90/03946 11 ; 206~08~

1 transistor 61, each of the latter having an emitter 2 connected through a corresponding 2K resistor 62, 63 to 3 the supply voltage Vcc. The bases of the transistors 60, 4 61 are common, and the collector of transistor 60 is connected to the collector of transistor 65 and the base 6 of transistor 57. An npn transistor 64 has its collec-7 tor connected to the base-csllector junction of the diode 8 61, and its emitter connected to the node 56. The base 9 of transistor 64 is common with the bases of npn lo transistors 65, 66, and with a node 67 at the base-11 emitter junction of a diode-connected npn transistor 68.
12 The emitter of transistor 65 is connected through a 650 13 ohm resistor 69 to the node 56, and-the emitters of the 14 transistor 66 and the diode-connected transistor 68 are connected directly to the node 56.

.
16 A startup circuit 70 comprises a lOOK resistor 72 17 connected in series with two diode-connected transistors 18 73, 74 to ground node 56, and a diode-connected 19 transistor 76 having its emitter connected to a node 77 between the collector of transistor 57 and a lsK~!resistor 21 78, which is connected at its other end to the node 67.
22 The collector-base junction of the diode 76 is connected 23 to a node 79 between the resistor 72 and the diode 73.

.., . , .~ . ~ , . .. . .
24 ;The bootstrap current source circuit 38 has the potential of operating at two-stable states, one in which there is 26 zero current flowing in the circuit, and the other in WO9l/01~94 PCT/US90/03946 206~8~ 12 1 which equal currents flow through the two branches of the 2 circuit. The startup circuit 70 serves to avoid the 3 zero-current state by insuring that some current always 4 flows in the transistors of the circuit 38, and the current gain does not fall to a very low value. If the 6 circuit 38 were near the zero-current state, the voltage 7 at the base of transistor 65 would be at or near ground, 8 and the voltage at the node 67 would be slightly above 9 ground as determined by leakage currents of the circuit.
lo The voltage at node 79 is two diode drops above ground, 11 therefore a voltage equal to about one diode drop would 12 appear across the resistor 78 through which a current 13 would flow into the transistors 64-66, which in turn 14 would cause current to flow in transistors 57, 60, 61, thereby avoiding the zero-current state. As the circuit 16 38 drives toward the desired stable state, the voltage 17 drop across the resistor 78 becomes large enough to 18 reverse bias the diode 76. - ' 19 The current source 39 comprises two LPNP transistors 80, 81, having their emitters connected,-respectively, 21 through a 2K resistor 82 and a lK resistor 83 to the 22 supply voltage Vcc. A lOOK resistor 84 is connected'from 23 Vcc to a node 85 between the bases of-the trànsistors 80, 24 81, a third LPNP transistor 86 having its emitter connected to the node 85. The collector of'transistor 86 26 is grounded, and its base is connected to the collector

27 of transistor 80 at a node 87, which is connected to the , wosl/o1s94 PCT/US9n/03946 13 206~0~
1 collector of transistor 66 in the bootstrap current 2 source 38. The collector of transistor 81 is connected 3 to an output node 88. The supply-independent reference 4 current developed in the current source 38 and flowing in the transistor 66 is mirrored in the transistor 81 and is 6 injected into the node 88 at the input of the band-gap 7 reference circuit 42.

8 The band-gap circuit develops a temperature-independent -9 reference voltage from the supply-independent current source 39. Details of the operation of the band-gap 11 circuit as well as other individual circuits such as the 12 current sources and current mirror circuits disclosed . 13 herein are well known and are not described herein. See, 14 for example, P. R. Gray and R. G. Meyer, Analysis and Design of Analog Integrated Circuits, Wiley, New York, 16 1984. .The band-gap reference circuit 42 comprises an npn 'r 17 transistor 90 having its base connected to the node 88, 18 its collector connected to the supply voltage ~cc and its 19 emitter connected.to an-output node 92 of the circuit 42.
20. The node 92 is connected through a 12K resistor 93 to a .. ..
21 node 94 connecting the base of an npn transistor 95 with 22 the collector of an npn transistor 96. The base of 23 transistor 96 is connected to the base-collector ~unction 24.. of ? ;diode-connected1transistor 97, which is-connëcted in series with-.a 5K resi-stor 98 between the output nodë 92 26 and ground. The emitter of transistor 95 is connected to .

WO~1/01594 PCT/US90/03946 20~4~85 14 1 ground, and the emitter of trancistor 96 is connected 2 through a 1.48K resistor 99 to ground.

3 Referring to FIG. 3 in conjunction with FIG. 1, a 4 representative one 44a of the band-gap referenced master current sources 44a..n and the corresponding current-6 mirror circuit 32a comprise an npn ~ransistor 102 having 7 its base connected to the output node 92 of the band-gap 8 reference circuit 42. The emitter of the transistor 102 9 is connected through the current-setting resistor 46a to ground, the resistor 46a having a value of 8.4K in the 11 instant representative circuit. The collector of 12 transistor 102 is connected to a node 105 of the current 13 mirror circuit 32a, which in turn is connected to the 14 base of an LPNP resistor 106, the collector of an LPNP
resistor 107 and through a 2K resistor 108 to the base of 16 transistor 107. The emitters of the transistors 106, 107 17 are connected, respectively, through lK resistors lo9, 18 110 to the supply voltage Vcc. The collector of 19 transistor 106 is connected to an output node 112, which can for example supply 50 microamps current by way of the 21 lead 30a to the corresponding current source 28a of 22 current mirror circuit 26a. The current developed in the 23 band-gap referenced master current source 44a, in this 24 instance 50 microamps, is mirrored-in the transistor 106 , ,, . . I
current source and supplied to the-functional circuit-26 group 20a (see FIG. 2) of the microcircuit chip 21 by way 27 of the bus 30a. The bias current requirement of each of ,.

-. ;: - . ~

WO~I/01594 PCT/US90/03946 ~ i~ 206~085 1 the functional circuit groups 20a..n is predetermined by 2 design and the appropriate value of current provided in 3 the design of the corresponding master current source 44a 4 by way of the current mirror circuits 32a..n. The currents are individually determined in the bias supply 6 circuit 10, which is essentially centrally located on the 7 microcircuit chip, and derived from a supply-independent 8 current source that is referenced to a temperature-9 independent voltage. The individual bias currents being distributed to the functional circuit areas throughout 11 the chip further makes the circuits less sensitive to-12 stlpply voltage variations due to line losses.

13 Multiple current sources 44a..n, which are connected to 14 and enabled by the band-gap voltage, produce biasing currents determined by the band-gap voltage and the 16 resistors 46a..n. The current-setting resistors 46a..n 17 are each chosen to match the type of resistor used in the 18 corresponding one of the functional circuit areas 20a..n 19 providing nominally constant gain and voltage~drops versus resistor tolerance. These biasing currents are 21 mirrored by current mirrors 32a..n and distributed to the 22 various functional circuits around the die for use as 23 local reference currents in current mirror circuits-24 25a..n local to the individual-circuits. -; --.,, , . , ~ - ~ . ; i When the power enable control signal PWRUP1 falls low, 26 base drive is removed from.the transistor 50 of the ...,.. ~.

WO9l/01594 PCr/l)S90/03946 `-- -20~n85 16 1 switch circuit 36 and its collector voltage floats up to 2 Vcc, which disables the reference current source 3~ and 3 shuts off drive current to the band-gap voltage source 4 42. The band-gap voltage then falls to ground turning off the various master current sources 44a..n and current 6 mirrors 32a..n, 26a..n, which removes bias current to the 7 functional circuit areas 20a..n and shuts off the system ; 8 circuits 12.

9 Referring to FIG. 4 in conjunction with FIG. 1, while the remote current mirror circuit 26a is shown in FIG. 1 as 11 having two elements, viz.: the local-reference current 12 source 28a and the current mirror element 24a, it is 13 understood that a remote current mirror 26m can include 14 two or more current mirror elements 24ma..mn, each of which mirrors the local reference current developed in 16 the current source 28m, by developing either a true 17 mirror of the reference current or a scaled current 18 proportional to the reference current, the magnitude of 19 the scaled currents being depending on the size of the - 20 current mirror 24ma... mn transistors relative to the size 21 of the current source 28m transistor.
., . ~ . . ~ ~ . .
..
22 All of the system circuits 12 are connected to the supply 23 voltage Vcc, therefore leakage currents will still flow 24 when the bias supply 10 is turned off by the switch circuit 36 as described above; if there are any signif-26 icant leakage paths in any the transistors of the system r ' WO91/01594 PCT~US9n/03946 206~085 1 circuits, which can number in the high hundreds, battery 2 degradation could occur at a faster rate than is 3 desirable. However, the process utilized to form the 4 circuits of the bias supply 10 and the system circuits 2Qa..n is the oxide-isolation process, which isolates the 6 collectors of the transistors from each other with 7 trenches etched into the epitaxial layer, the trenches 8 being lined with silicon dioxide and filled with 9 polycrystalline silicon, the process yielding circuits with very low leakage current. Consequently, when the ll desired bias currents are shut off by disabling the 12 PWRUPl signal, the leakage current, from all 700 to 800 13 transistors in the system, is very low--on the order of 14 nanoamps. Circuits built with conventional junction isolation processes would also benefit from this 16 technique; however, the magnitude of the off current 17 would not be as low.

18 Referring to the FIG. 5 timing diagram, it is seen that l9 system current IVcc,-from system turn-off time ~to when the PWRUPl signal is disabled, decays from 15 ma to 21 essentially zero current, less than lOO nanoamps, within 22 300 microseconds. Naturally, the exact figures are 23 circuit dependent and the invention will operate in other 24 environments. ~

In summary one embodiment of the invention provides a 26 microcircuit bias supply capable of an intermittent duty-W~91/01594 2 0 ~ ~ 0 8 5 PCT/US90/03946 1 cycle under external control. T~e bias supply generates 2 circuit bias derived from a current source referenced to 3 a voltage-reference circuit, which in turn is provided 4 with operating current from a reference current source circuit coupled to an on/off circuit that disables the 6 reference current source, which switches off the bias 7 current to the microcircuits, whereby only leakage 8 current flows during quiescent periods. The 9 microcircuits can for example be implemented in oxide-isolated bipolar integrated circuits.

11 A second embodiment of the invention provides, a 12 microcircuit bias supply capable of an intermittent duty-13 cycle under external control generates circuit bias 14 mirrored from a reference current source, and supplies the bias current to a functional circuit on the chip.
16 The current is mirrored in the functional circuit and 17 distributed therein. A switch circuit disables the 18 reference current source during power-off portions of the 19 microcircuit duty cycle, which switches off the bias current to the microcircuits, whereby only leakage 21 current flows during quiescent periods. ~ -22 An imnportant aspect ofg the present invention is that -23 the functional circuit current bias supply circuits are 24 controlled from the voltage reference through current mirrors and hence they operate at a voltage which is 26 relatively near ground potential. The entire supply ; 20~085 1 voltage (except for the drop across the bias supply 2 circl~its) is available to the application circuits.
3 The current bias circuits are required for bias purposes 4 regardless of what type of turn off circuitry is used, hence, the voltage drop across the bias circuit is not a 6 penalty incurred by the use of the turn off circuit of 7 the present invention.

8 While the principles of the invention have now been made 9 clear in the foregoing illustrative embodiment, there will be immediately obvious to those skilled in the art 11 many modifications of structure, arrangement, 12 proportions, the elements, material and components used 13 in the practice of the invention, and otherwise, which 14 are particularly adapted for specific environments and operating requirements without departing from those 16 principles. The appended claims are, therefore, intended 17 to cover and embrace any such modifications, within the 18 limits only of the true spirit and scope of the 19 invention.

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Claims (18)

Claims

1. A microcircuit having a plurality of microcircuit elements, and comprising:
a voltage source supplying operating voltage to the microcircuit;
a functional circuit connected to the voltage source;
means connected to the voltage source for generating a bias current for operating the functional circuit;
and means for disabling the bias current generating means thereby shutting off the bias current to the functional circuit, whereby power dissipation in the microcircuit is limited to leakage currents of the plurality of microcircuit elements.

2. The microcircuit of claim 1 wherein the bias current generating means comprises:
a current source connected to the voltage source and generating a reference current;
a current mirror circuit coupled to the functional circuit, the current mirror circuit generating the bias current from the reference current.

3. The microcircuit of claim 1 wherein the bias current generating means comprises:
a first current source connected to the voltage source and generating a reference current;

a reference-voltage circuit receiving the reference current and generating a reference voltage;
a second current source coupled to the functional circuit and referenced to the reference voltage, the second current source generating the bias current.

4. The microcircuit of claim 3 wherein the first current source comprises a self-biased current source.

5. The microcircuit of claim 3 wherein the reference-voltage circuit comprises a band-gap reference voltage generator circuit.

6. The microcircuit of claim 3 wherein the disabling means comprises a transistor switch supplying a ground return for the first current source and receiving a power on/off control signal from an external source.

7. The microcircuit of claim 3 wherein the disabling means comprises a transistor switch supplying a ground return for only the first current source and receiving a power on/off control signal from an external source.

8. A microcircuit having a plurality of microcircuit elements and comprising:

a source of voltage supplying operating voltage to the microcircuit;
a functional circuit connected to the voltage source; and a bias-current circuit including a first current source connected to the voltage source and generating a reference current;
a reference-voltage circuit receiving the reference current and generating a reference voltage;
a second current source coupled to the functional circuit and referenced to the reference voltage, the second current source generating a predetermined magnitude of bias current suitable for operating the functional circuit; and means for switching the bias-current circuit to a quiescent state thereby disabling the functional circuit, whereby power dissipation in the microcircuit is limited to leakage currents of the microcircuit elements.

9. The microcircuit of claim 8 wherein the switching means, when enabled, supplies a return for the first current source, and when disabled, opens the return thereby disabling the first current source.

10. The microcircuit of claim 8 wherein the switch means comprises a transistor receiving a power on/off control signal from an external source.

11. The microcircuit of claim 8 wherein the microcircuit elements are implemented in oxide-isolated bipolar integrated circuits.

12. The microcircuit of claim 8, further comprising a third current source connected to the voltage source and coupled between the first current source and the reference-voltage circuit, the third current source generating a mirror of the reference current.

13. A microcircuit having a plurality of microcircuit elements and comprising:
a source of voltage supplying operating voltage to the microcircuit;
a plurality of functional circuits connected to the voltage source, each including a current mirror circuit;
a bias-current circuit including a first current source connected to the voltage source and generating a reference current;
a reference-voltage circuit receiving the reference current and generating a reference voltage;
a plurality of second current sources corresponding with the plurality of functional circuits, each of the plurality of second current sources being referenced to the reference voltage and each generating a bias current of predetermined magnitude suitable for operating the corresponding one of the plurality of functional circuits;
a plurality of second current-mirror circuits, each connected to a corresponding one of the current-mirror circuits in the plurality of functional circuits, each of the predetermined bias currents of the second current sources being mirrored in the corresponding second current-mirror circuit of the bias-current circuit and in turn the current-mirror circuit of the corresponding functional circuit; and means for switching the bias-current circuit to a quiescent state thereby disabling the plurality of functional circuits, whereby power dissipation in the misrocircuit is limited to leaXage currents of the microcircuit elements.

14. The microcircuit of claim 13 wherein the switching means, when enabled, supplies a return for the first current source, and when disabled, opens the return thereby disabling the first current source.

15. The microcircuit of claim 14 wherein the switching means comprises a transistor receiving a power on/off control signal from an external source.

16. The microcircuit of claim 13 wherein the microcircuit elements are implemented in oxide-isolated bipolar integrated circuits.

17. The microcircuit of claim 13, further comprising a third current source connected to the voltage source and coupled between the first current source and the reference-* voltage circuit, the third current source generating a mirror of the reference current.

18. A microcircuit having a plurality of microcircuit elements implemented in oxide-isolated bipolar integrated circuits, and comprising:
a voltage source supplying operating voltage to the microcircuit;
a functional circuit connected to the voltage source;
a bias-current circuit including a first self-biased current source connected to the voltage source and generating a first reference current;
a band-gap reference-voltage circuit receiving the reference current and generating a reference voltage;
a second current source coupled to the functional circuit and referenced to the reference voltage, the second current source generating a predetermined magnitude of bias current suitable for operating the functional circuit; and a transistor switch receiving a power on-off control signal from an external source and supplying a return path for the self-biased current source when in an on state, the self-biased current source being disabled when the switch is in an off state thereby disabling the functional circuit, whereby power dissipation in the microcircuit is limited to leakage currents of the plurality of microcircuit elements.